Dengue fever (pronounced den-gay) and dengue hemorrhagic fever (DHF) are acute fever diseases which occur in the tropics from mosquitoes. These diseases can be life-threatening, and are caused by four closely related virus serotypes of the genus Flavivirus, family Flaviviridae. It is also known as breakbone fever, since it can be extremely painful. It occurs widely in the tropics,
Unlike malaria, dengue is just as common in the urban districts as in rural areas. Each serotype is sufficiently different that there is no cross-protection and epidemics caused by multiple serotypes (hyperendemicity) can occur. Dengue is transmitted to people by the Aedes (Stegomyia) aegypti or more rarely the Aedes albopictus mosquito, both of which feed exclusively during daylight hours.
Some 2.5 billion people, two fifths of the world’s population, are now at risk from dengue and estimates that there may be 50 million cases of dengue infection worldwide every year. The disease is now endemic in more than 100 countries. There was a serious outbreak in Rio de Janeiro in February 2002 affecting around one million people and killing sixteen.
The disease has symptoms of fever, with a sudden onset of headache, muscle and joint pains (myalgias and arthralgias—severe pain that gives it the nickname break-bone fever or bonecrusher disease) and rash. The classic dengue rash is a generalized maculopapular rash with islands of sparing. A hemorrhagic rash of characteristically bright red pinpoint spots, known as petechiae can occur later during the illness and is associated with thrombocytopenia. It usually appears first on the lower limbs and the chest; in some patients, it spreads to cover most of the body. There may also be severe pain from behind the eyes that is distinctive to dengue infections, and gastritis with some combination of associated abdominal pain, nausea, vomiting, congealed blood, or diarrhea. Some cases develop much milder symptoms which can be misdiagnosed as influenza or other viral infection when no rash or pain is present. Travelers with the fever from tropical areas may transmit dengue inadvertently to previously dengue-free populations of mosquitoes if they have not been properly diagnosed for dengue. Patients only transmit dengue when they have fever after being bitten by Aedes (Stegomyia) Aegypti mosquitoes, or (much more unusually) via blood products.
Usually dengue fever lasts around two to seven days, with a smaller peak of fever at the trailing end of the disease. Clinically, the blood cell count will drop until after the patient’s temperature is normal. Cases of dengue hemorrhagic fever also show higher fever, variable hemorrhagic phenomena including bleeding from the eyes, into the gut, and oozing blood from skin pores, thrombocytopenia, and hemoconcentration. When Dengue infections proceed to DHF symptoms, DHF causes vascular leak syndrome which includes fluid in the blood vessels leaking through the skin and into spaces around the lungs and belly. This fluid loss and severe bleeding can cause blood pressure to fall, then Dengue Shock Syndrome (DSS) sets in, which has a high mortality rate.
The diagnosis of dengue is usually made clinically. The usual pattern is a high fever with no localizing source of infection, a rash with thrombocytopenia and relative leukopenia – low platelet and white blood cell count. Dengue infection can affect many organs and thus may present unusually as liver dysfunction, renal impairment, meningo-encephalitis or gastroenteritis.
There is no tested and approved vaccine for the dengue flavivirus but there are many ongoing vaccine development programs. The mainstay of treatment is timely supportive therapy to tackle circulatory shock due to hemoconcentration and bleeding. Close monitoring of vital signs in the critical period (up to 2 days after defervescence – the departure or subsiding of a fever) is critical. Increased oral fluid intake is recommended to prevent dehydration. Supplementation with intravenous fluids may be necessary to prevent dehydration and significant concentration of the blood if the patient is unable to maintain oral intake. Aspirin and non-steroidal anti-inflammatory drugs should be avoided as these drugs may worsen the bleeding tendency associated with some of these infections. Patients may receive paracetamol preparations to deal with these symptoms if dengue is suspected.
Dengue may also be transmitted via infected blood products (blood transfusions, plasma, and platelets), and in countries such as Singapore, where dengue is endemic, the risk was estimated to be between 1.6 and 6 per 10,000 blood transfusions.
I’ve been in Costa Rica since December of 2008 and so far, luckily, I have managed to avoid dengue fever. However, I know several people who have had it and it’s a nasty experience. Try to avoid being out in dusk in areas of wet, long grass, and use Off!